How this map was made:

Daily non-zero values of snowfall and liquid water equivalent within a given month were ratioed based on the entire length of record for each station (which is variable between stations). An average was then computed from the individual daily values to obtain a snow water equivalent for each station. The ratios were then gridded using a kriging technique. Higher ratios indicate wetter snow events (high liquid water content) while lower ratios represent drier snow events (low liquid water content). Quality control was performed to eliminate sources of error, such as days with a mixed precipitation type (yielding anomalously high ratio), or stations with very few daily observations.